check this links maybe help you

http://www.fao.org/3/t0551e/t0551e08.htm

Article Sewage sludge for sustainable agriculture: Contaminants’ con...

https://www3.epa.gov/npdes/pubs/sludge.pdf

http://www.nuigalway.ie/media/gene/files/Colon-et-al.-COST.pdf

Supposing test the heavy metals contents in sewage sludge

Biological load and heavy metals such as

Copper , Nickel , Zinc, Cadmium , Lead, Mercury and Chromium.

N, NO3, NO3, NH4, P, K, Na, Mg, Cu, Ni, Zn, Pb, Cr, Hg, OC, DM, etc.

yo will be analized heavy metals

contaminants such are heavy metals are the big issue of using sewage sludge, another parameters is also good NO3, NH4-N etc

The sewage must contsin high level of minersl NPK alow level of havey mineral to use as fertilizer for agriculture and also must test these mineral